1. Field of the Invention
The present invention relates generally to a high-performance fingerprint image-processing method, and more particularly to a fingerprint image-processing method that uses the orientation-based line spatial filter and rhombus spatial filter as a tool to enhance the image in accordance with the fingerprint direction of fingerprint at each point.
2. Description of the Prior Arts
The development with respect to the technology of fingerprint recognition has been benefited from the electronic-integrated manufacturing technology and the researches toward a fast & reliable algorithm in association with a generation of hefty volume of data for recognition; therein, the procedure of fingerprint recognition system currently in existence is shown in the FIG. 6, and in one word, it indicates that the fingerprint recognition technology mainly relates to the fingerprint reading, image processing, minutiae extraction, data acquisition and matching. As shown in the figure, the image-processing technology; wherein, after acquiring the fingerprint image that is read from the human body through a fingerprint reading device, a further processing will follow to enhance the original image so that a clearer, low noise and high quality fingerprint image is obtainable; meanwhile, the quality of processed image will directly affect the fingerprint recognition rate; and generally speaking, the degradation of fingerprint image caused by the factors of external environment often leads to problems in minutiae extraction at the terminal and the bifurcation; for instances, a dry finger may cause broken or incomplete ridges to the center of fingerprint image that may be judged as islands during the feature extraction; and that is the reason why the originally acquired fingerprint images need to be further processed with an image enhancement for remedy of broken and incomplete ridges and with a filtering of noise in a bid to lessen the Fault Acceptance Rate (FAR) and Fault Rejection Rate (FRR) for fingerprint identification.
In accordance with the prior art, the technology of Gray-Scale Fingerprint Image Enhancement has two primary approaches in this regard; one of the approaches is to use the process of Fourier transform or the Wavelet transform, etc. to transform the image from the spatial domain to the frequency domain, perform a mask filtering in accordance with the frequency distribution and direction, and then transform it back to the spatial domain; apparently thus doing frequently is time-consuming when transforming the image back and forth between the spatial domain and the frequency domain, and unable to undertake the individual enhancement mainly focusing on every point and ridge in different direction in the spatial domain; instead, it has to perform an enhancement in all directions in the frequency domain and then to further select the correct directions to enhance the result in the spatial domain; such an operation takes a lot of time and occupy a great capacity of memory.
The other commonly used approach of Gray Scale Fingerprint Image Enhancement is to enhance the image directly in the spatial domain; for example, the Gabor like anisotropic filtering, Gaussian like mask for filtering or parallel ridge filtering; these spatial filtering masks generally have to go through many intricate processes to obtain the outcome while thus task is very time-consuming and usually needs to use a large mask space; not large enough mask space may result in a lower enhancing effect; that is to say, if the outcome of image enhancement is made by using merely a simple mask, then the connectivity at the breakpoints is usually much lower than the outcome from the enhancement in frequency domain; besides, if using a large mask space, then a problem of occupying too much memory capacity must occur consequently.